When a hand-held tool, such as a power drill, is used for the boring of a hole in a wall, a workpiece, or the like, it often is difficult for the user to maintain the drill in a position in which the axis of the hole forms a desired angle with a horizontal or vertical plane. For example, if it is desired to drill a hole in a vertical wall so that the axis of the hole is perpendicular to the wall, the axis of the drill at all times must be maintained in a position that is perpendicular to the wall surface. Not many persons are sufficiently skilled to be able to distinguish between true perpendicularity and slight deviations therefrom. In those instances in which the axis of a drilled hole is at some angle other than normal to a horizontal or vertical plane, it is even more difficult for the user of a hand-held tool to orient and maintain the tool at the proper position of angularity.
The difficulties encountered in positioning and maintaining a hand-held tool at a selected position of angularity also exist in connection with tools supported on adjustable brackets, and the like, although to a lesser extent inasmuch as jigs or fixtures can be used to locate the tool initially at the desired angularity. However, during use of such a tool it sometimes happens that the adjustable jig or fixture slips or otherwise changes position. Sometimes the changes in position may be noted visually but oftentimes the changes are undetected.
Apparatus constructed in accordance with the invention includes a spirit level that is adapted for attachment to any tool of the class referred to and is universally adjustable relative to the tool so as to enable the tool to be located in any one of a number of selected positions of angularity and maintained in such position by visual reference to the spirit level.